The present invention relates in general to an electric brake controller for energizing electrically operated brakes in a towed vehicle and, in particular, to an electric brake controller which incorporates a means for sensing the deceleration of the towing vehicle and for generating a brake energizing signal as a function of the deceleration.
Recreational and utility trailers adapted to be towed by automobiles and small trucks and many similar towed vehicles are commonly provided with electric brakes. The electric brakes generally comprise a pair of brake shoes which, when actuated, frictionally engage a brake drum. An electromagnet is mounted on one end of a lever coupled to actuate the brake shoes. When an electric current is applied to the electromagnet, the electromagnet is drawn against the rotating brake drum which pivots the lever to actuate the brakes. Typically, the braking force produced by the brake shoes is proportional to the electric current applied to the electromagnet.
To ensure proper operation, a control system for electrically operated brakes must be easily adjustable to accommodate different relative weights of the towed and towing vehicles. Also, the control system must be predictable to give the driver of the towing vehicle a feeling of smooth and positive brake operation both upon applying and releasing the brakes in the towing vehicle.
In one type of electronic brake control system, such as the system disclosed in U.S. Pat. No. 4,295,687, the electric brakes are actuated in response to the operation of the towing vehicle's brake pedal by the driver. In this system, a transducer produces a brake control signal corresponding to the desired braking effort by sensing either (1) the hydraulic pressure in the braking system of the towing vehicle or (2) the pressure applied by a driver's foot to the towing vehicle's brake pedal. A pulse width modulator is responsive to the brake control signal for generating a fixed frequency pulsed output signal having a duty cycle proportional to the amount of braking effort desired.
Various towed vehicle braking systems have been proposed wherein the braking of the trailer is automatically controlled by the sensing of deceleration forces. For example, U.S. Pat. Nos. 2,242,153; 2,642,961; 2,779,443; 2,856,036; and 2,969,857 all disclose automatic brake applying systems wherein the deceleration inertial force imposed upon the hitch by the trailer during deceleration of a towing vehicle is sensed and used to effect braking of the trailer.
Also, it has been proposed to use a pendulum or a mass movement sensing device for sensing the deceleration of a towing vehicle and for operating either a mechanical or an electrical braking system in the towed vehicle. Examples of such pendulum systems are disclosed in U.S. Pat. Nos. 2,870,876 and 3,053,348.
One type of electronic brake controller which includes a pendulum unit for sensing the deceleration of the towing vehicle is disclosed in U.S. Pat. No. 3,953,084. In this patent, the pendulum is provided with a shield to block the passage of light from a light source to a light sensing unit when the pendulum is in a resting position. When the brakes of the towing vehicle are operated and the vehicle decelerates, the pendulum will swing to permit light to fall on the light sensing unit which then generates a control signal. The brake controller is responsive to the control signal for producing a pulsed output signal having a fixed frequency and a variable pulse width proportional to the level of the control signal.